In general, a spark plug for use in an internal combustion engine includes a tubular metal shell, a tubular insulator that is disposed in an inner hole of the metal shell, a center electrode that is disposed in an axial hole of the insulator at a tip end side, a terminal electrode that is disposed in the axial hole at the other end side, and a ground electrode of which one end is connected to a tip end of the metal shell and the other end faces the center electrode and forms a spark discharge gap. Furthermore, a spark plug is also known in which a resistor is provided between a center electrode and a terminal electrode inside an axial hole for the purpose of preventing radio wave noise generated in accordance with an operation of an engine.
In recent years, in connection with an increase in an output of the internal combustion engine, an increase in a discharge voltage of the spark plug has been required. If the discharge voltage of the spark plug is increased, high frequency noise generated during discharging increases and there is a concern that high frequency noise brings a bad influence to an electronic control device of a vehicle. Thus, it is preferable that high frequency noise of the spark plug is reduced.
In order to reduce high frequency noise during discharging of the spark plug, various techniques are proposed in the related art. For example, JP-A-2011-159475 discloses a configuration in which a noise reduction member formed of a cylindrical ferrite is provided so as to surround a periphery of a conductor passing through an inside of a spark plug. Furthermore, JP-A-H02-284374 discloses a configuration in which wiring is provided an inside of a spark plug.
Further improvement in a material or a shape of a conductive member electrically connecting between the center electrode and the terminal electrode in the axial hole, so as to reduce high frequency noise is desirable.
The invention is provided to address the problems described above and can be realized in the following aspects.